Electrochromic device containing color-tunable nanostructures

ABSTRACT

An electrochromic device and method, the device including: a first transparent conductor layer; a working electrode disposed on the first transparent conductor layer and including nanostructures; a counter electrode; a solid state electrolyte layer disposed between the counter electrode and the working electrode; and a second transparent conductor layer disposed on the counter electrode. The nanostructures may include transition metal oxide nanoparticles and/or nanocrystals configured to tune the color of the device by selectively modulating the transmittance of near-infrared (NIR) and visible radiation as a function of an applied voltage to the device.

FIELD

The present invention is generally directed to electrochromic devices,and more particularly to the selectively modulating transmittance ofradiation as a function of voltage applied to a nanostructured materialin an electrochromic device.

BACKGROUND OF THE INVENTION

Residential and commercial buildings represent a prime opportunity toimprove energy efficiency and sustainability in the United States. Thebuildings sector alone accounts for 40% of the United States' yearlyenergy consumption (40 quadrillion BTUs, or “quads”, out of 100 total),and 8% of the world's energy use. Lighting and thermal management eachrepresent about 30% of the energy used within a typical building, whichcorresponds to around twelve quads each of yearly energy consumption inthe US. Windows cover an estimated area of about 2,500 square km in theUS and are a critical component of building energy efficiency as theystrongly affect the amount of natural light and solar gain that enters abuilding. Recent progress has been made toward improving window energyefficiency through the use of inexpensive static coatings that eitherretain heat in cold climates (low emissive films) or reject solar heatgain in warm climates (near-infrared rejection films).

Currently, static window coatings can be manufactured at relatively lowcost. However, these window coatings are static and not well suited forlocations with varying climates. An electrochromic (EC) window coatingovercomes these limitations by enhancing the window performance in allclimates. EC window coatings undergo a reversible change in opticalproperties when driven by an applied potential. Traditional ECmaterials, such as WO₃, Nb₂O₅, and NiO, primarily modulate radiation inthe visible spectral region, while radiation in the near-infrared (NIR)spectral region remains either unchanged or switches simultaneously withvisible region of light. Further, performance of electrochromicmaterials may degrade from use over time as a result of repeatedexposure to radiation in the ultraviolet (UV) spectral region.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present disclosure are directed to anelectrochromic device comprising: a first transparent conductor layer; aworking electrode disposed on the first transparent conductor layer andcomprising nanostructures comprising from about 40 to about 80 wt. % ofamorphous niobium oxide nanoparticles and from about 60 to about 20 wt.% of the cesium doped tungsten oxide nanoparticles having a cubiccrystal lattice structure, based on the total weight of thenanostructures; a counter electrode; a solid state electrolyte layerdisposed between the counter electrode and the working electrode; and asecond transparent conductor layer disposed on the counter electrode.

Exemplary embodiments of the present disclosure are directed to anelectrochromic device comprising: a first transparent conductor layer; aworking electrode disposed on the first transparent conductor layer andcomprising nanostructures configured such that the electrochromic devicetransmits light of a first color in a bright mode and a second color ina dark mode; a counter electrode; a solid state electrolyte layerdisposed between the counter electrode and the working electrode; and asecond transparent conductor layer disposed on the counter electrode,wherein at least one of the first color and the second color is disposedin a first Lab color coordinate box having A* color coordinates rangingfrom about zero to about −4.0, and B* color coordinates ranging fromabout 4.0 to about −2.0. The Lab color coordinates refer to thecoordinates in the CIELAB color space.

Exemplary embodiments of the present disclosure are directed to a methodof operating an electrochromic device, comprising: operating the devicein a bright mode, such that the device transmits light of a first color;and operating the device in a second mode, such that the devicetransmits light of a second color, wherein at least one of the firstcolor and the second color is disposed in a first Lab color coordinatebox having A* color coordinates ranging from about zero to about −4.0,and B* color coordinates ranging from about 4.0 to about −2.0.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic representations of electrochromic devicesaccording to various embodiments.

FIG. 2 is a schematic representation of an electrochromic device thatmay be tuned to produce a particular color, according to variousembodiments or the present disclosure.

FIG. 3A includes photographs of electrochromic devices including workingelectrodes having the various amounts of NbO_(x) nanoparticles andcorresponding amounts CsW₂O₆ nanocrystals.

FIG. 3B is a graph showing the color spectra of light transmittedthrough corresponding electrochromic devices of FIG. 3A.

FIGS. 4A and 4B are photographs of a fabricated electrochromic device180A in a bright mode and a dark mode, according to various embodiments.

FIG. 4C is a graph illustrating bright mode and dark mode transmittanceof the electrochromic device of FIGS. 4A and 4B.

FIGS. 5A and 5B are respectively photographs of an electrochromic devicein a bright mode and a dark mode, according to various embodiments ofthe present disclosure.

FIG. 5C is a graph illustrating bright mode, transition mode, and darkmode transmittance of the electrochromic device of FIGS. 5A and 5B.

FIGS. 6A and 6B are Lab color coordinate graphs respectively showing atransmission target color coordinate box and an outdoor reflection colorcoordinate box, corresponding to an electrochromic device having aneutral gray color, according to various embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown. This invention may, however, be embodied in many differentforms and should not be construed as limited to the exemplaryembodiments set forth herein. Rather, these exemplary embodiments areprovided so that this disclosure is thorough, and will fully convey thescope of the invention to those skilled in the art. In the drawings, thesize and relative sizes of layers and regions may be exaggerated forclarity. Like reference numerals in the drawings denote like elements.

It will be understood that when an element or layer is referred to asbeing disposed “on” or “connected to” another element or layer, it canbe directly on or directly connected to the other element or layer, orintervening elements or layers may be present. In contrast, when anelement is referred to as being disposed “directly on” or “directlyconnected to” another element or layer, there are no interveningelements or layers present. It will be understood that for the purposesof this disclosure, “at least one of X, Y, and Z” can be construed as Xonly, Y only, Z only, or any combination of two or more items X, Y, andZ (e.g., XYZ, XYY, YZ, ZZ).

Various embodiments disclosed herein provide electrochromicnanostructured materials capable of selectively modulating radiation innear-infrared (NIR) and visible spectral regions. The material mayinclude nanostructured doped transition metal oxides with ternarycompounds of the type A_(x)M_(z)O_(y). In various embodimentA_(x)M_(z)O_(y) compounds, if it is assumed that z=1, then 0.08≦x≦0.5(preferably 0.25≦x≦0.35), and 2≦y≦3. In various embodiments, since thenanostructures may be non-uniform as a function of depth, x mayrepresent an average doping content. To operate, the subject materialmay be fabricated into an electrode that will change optical propertiesafter driven by an applied voltage.

In order to improve the performance of EC window coatings, selectivemodulation of NIR and visible spectra radiation, and avoidance ofdegrading effects of UV radiation, may be desired. Various embodimentsmay provide single-component electrochromic nanostructured materialscapable of selectively modulating NIR and visible spectral regions.Further, since certain spectral regions may damage the electrochromicnanostructured material, the various embodiments may incorporate atleast one protective material and/or protective layer to prevent suchdamage.

The various embodiments provide devices and methods for enhancingoptical changes in windows using electrochromic nanostructured materialsfabricated into an electrode to form an electrochromic device. Invarious embodiments, the material may undergo a reversible change inoptical properties when driven by an applied potential. Based on theapplied potential, the electrochromic nanostructured materials maymodulate NIR radiation (wavelength of around 780-2500 nm), as well asvisible radiation (wavelength of around 400-780 nm). In an example, thedevice may include a first nanostructured material that modulatesradiation in a portion of the NIR spectral region and in the visiblespectral region, and a second nanostructured material that modulatesradiation in an overlapping portion of the NIR spectral region such thatthe NIR radiation modulated by the device as a whole is enhanced andexpanded relative to that of just the first nanostructured material. Invarious embodiments, the material may operate in multiple selectivemodes based on the applied potential.

Further, the various embodiments may include at least one protectivematerial to prevent or reduce damage to an electrochromic nanostructuredmaterial that may result from repeated exposure to radiation in the UVspectral region. In an example, a protective material may be used toform at least one barrier layer in the device that is positioned toblock UV radiation from reaching the first nanostructured material andelectrolyte. In another example, a protective material may be used toform a layer that is positioned to block free electron or hole chargecarriers created in the electrolyte due to absorption of UV radiation bythe nanostructured electrode material from migrating to that material,while allowing conduction of ions from the electrolyte (i.e., anelectron barrier and ion conductor).

In various embodiments, control of individual operating modes formodulating absorption/transmittance of radiation in specific spectralregions may occur at different applied biases. Such control may provideusers with the capability to achieve thermal management within buildingsand other enclosures (e.g., vehicles, etc.), while still providingshading when desired.

FIGS. 1A-1C illustrate embodiment electrochromic devices. It should benoted that such electrochromic devices may be oriented upside down orsideways from the orientations illustrated in FIGS. 1A-1C. Furthermore,the thickness of the layers and/or size of the components of the devicesin FIGS. 1A-1C are not drawn to scale or in actual proportion to oneanother other, but rather are shown as representations.

In FIG. 1A, an embodiment electrochromic device 100 may include a firsttransparent conductor layer 102 a, a working electrode 104, a solidstate electrolyte 106, a counter electrode 108, and a second transparentconductor layer 102 b. Some embodiment electrochromic devices may alsoinclude one or more optically transparent support layers 110 a, 110 brespectively positioned in front of the first transparent conductorlayer 102 a and/or positioned behind the second transparent conductorlayer 102 b. The support layers 110 a, 110 b may be formed of atransparent material such as glass or plastic.

The first and second transparent conductor layers 102 a, 102 b may beformed from transparent conducting films fabricated using inorganicand/or organic materials. For example, the transparent conductor layers102 a, 102 b may include inorganic films of transparent conducting oxide(TCO) materials, such as indium tin oxide (ITO) or fluorine doped tinoxide (FTO). In other examples, organic films in transparent conductorlayers 102 a, 102 b may include graphene and/or various polymers.

In the various embodiments, the working electrode 104 may includenanostructures 112 of a doped transition metal oxide bronze, andoptionally nanostructures 113 of a transparent conducting oxide (TCO)composition shown schematically as circles and hexagons for illustrationpurposes only. As discussed above, the thickness of the layers of thedevice 100, including and the shape, size and scale of nanostructures isnot drawn to scale or in actual proportion to each other, but isrepresented for clarity. In the various embodiments, nanostructures 112,113 may be embedded in an optically transparent matrix material orprovided as a packed or loose layer of nanostructures exposed to theelectrolyte.

In the various embodiments, the doped transition metal oxide bronze ofnanostructures 112 may be a ternary composition of the type AxMzOy,where M represents a transition metal ion species in at least onetransition metal oxide, and A represents at least one dopant. Transitionmetal oxides that may be used in the various embodiments include, butare not limited to any transition metal oxide which can be reduced andhas multiple oxidation states, such as niobium oxide, tungsten oxide,molybdenum oxide, vanadium oxide, titanium oxide and mixtures of two ormore thereof. In one example, the nanostructured transition metal oxidebronze may include a plurality of tungsten oxide (WO_(3-x))nanoparticles, where 0≦x≦0.33, such as 0≦x≦0.1.

In various embodiments, the at least one dopant species may be a firstdopant species that, upon application of a particular first voltagerange, causes a first optical response. The applied voltage may be, forexample, a negative bias voltage. Specifically, the first dopant speciesmay cause a surface plasmon resonance effect on the transition metaloxide by creating a significant population of delocalized electroniccarriers. Such surface plasmon resonance may cause absorption of NIRradiation at wavelengths of around 780-2000 nm, with a peak absorbanceat around 1200 nm. In various embodiments, the specific absorbances atdifferent wavelengths may be varied/adjusted based other factors (e.g.,nanostructure shape, size, etc.), discussed in further detail below. Inthe various embodiments, the first dopant species may be an ion speciesselected from the group of cesium, rubidium, and lanthanides (e.g.,cerium, lanthanum, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, and lutetium).

In various embodiments, the dopant may include a second dopant speciesthat causes a second optical response based upon application of avoltage within a different, second particular range. The applied voltagemay be, for example, a negative bias voltage. In an embodiment, thesecond dopant species may migrate between the solid state electrolyte106 and the nanostructured transition metal oxide bronze of the workingelectrode 104 as a result of the applied voltage. Specifically, theapplication of voltage within the particular range may cause the seconddopant species to intercalate and deintercalate the transition metaloxide structure. In this manner, the second dopant may cause a change inthe oxidation state of the transition metal oxide, which may cause apolaron effect and a shift in the lattice structure of the transitionmetal oxide. This shift may cause absorption of visible radiation, forexample, at wavelengths of around 400-780 nm.

In various embodiments, the second dopant species may be anintercalation ion species selected from the group of lanthanides (e.g.,cerium, lanthanum, praseodymium, neodymium, promethium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, and lutetium), alkali metals (e.g., lithium, sodium,potassium, rubidium, and cesium), and alkali earth metals (e.g.,beryllium, magnesium, calcium, strontium, and barium). In otherembodiments, the second dopant species may include a charged protonspecies.

In various embodiments, nanostructures 113 may optionally be mixed withthe doped transition metal oxide bronze nanostructures 112 in theworking electrode 104. In the various embodiments, the nanostructures113 may include at least one TCO composition, which prevents UVradiation from reaching the electrolyte and generating electrons. In anexample embodiment, the nanostructures 113 may include an indium tinoxide (ITO) composition, which may be a solid solution of around 60-95wt % (e.g., 85-90 wt %) indium(III) oxide (In₂O₃) and around 5-40 wt %(e.g., 10-15 wt %) tin(IV) oxide (SnO₂). In another example embodiment,the nanostructures 113 may include an aluminum-doped zinc oxide (AZO)composition, which may be a solid solution of around 99 wt % zinc oxide(ZnO) and around 2 wt % aluminum(III) oxide (Al₂O₃). Additional oralternative TCO compositions that may be used to form nanostructures 113in the various embodiments include, but are not limited to, indiumoxide, zinc oxide and other doped zinc oxides such as gallium-doped zincoxide and indium-doped zinc oxide.

The TCO composition of nanostructures 113 may be transparent to visiblelight and, upon application of the first voltage, may modulateabsorption of NIR radiation at wavelengths of around 1200-2500 nm, withpeak absorbance around 2000 nm (e.g., at a longer peak wavelength thanthe bronze nanoparticles 112, but with overlapping absorption bands). Inparticular, application of the first voltage may cause an increase infree electron charge carriers, and therefore cause a surface plasmonresonance effect in at least one TCO composition of nanostructures 113.In an embodiment in which the TCO composition is ITO, the surfaceplasmon resonance effect may be caused by oscillation of free electronsproduced by the replacement of indium ions (In³⁺) with tin ions (Sn⁴⁺).Similar to the transition metal oxide bronze, such surface plasmonresonance may cause a change in absorption properties of the TCOmaterial. In some embodiments, the change in absorption properties maybe an increase in absorbance of NIR radiation at wavelengths thatoverlaps with that of the nanostructures 112. Therefore, the addition ofTCO composition nanostructures 113 to the working electrode 104 mayserve to expand the range of NIR radiation absorbed (e.g., atwavelengths of around 780-2500 nm) compared to that of thenanostructures 112 alone (e.g., at wavelengths of around 780-2000 nm),and to enhance absorption of some of that NIR radiation (e.g., atwavelengths of around 1200-2000 nm).

Based on these optical effects, the nanostructure 112 and optionalnanostructure 113 of the working electrode may progressively modulatetransmittance of NIR and visible radiation as a function of appliedvoltage by operating in at least three different modes. For example, afirst mode may be a highly solar transparent (“bright”) mode in whichthe working electrode 104 is transparent to NIR radiation and visiblelight radiation. A second mode may be a selective-IR blocking (“cool”)mode in which the working electrode 104 is transparent to visible lightradiation but absorbs NIR radiation. A third mode may be a visibleblocking (“dark”) mode in which the working electrode 104 absorbsradiation in the visible spectral region and at least a portion of theNIR spectral region. In an example, application of a first voltagehaving a negative bias may cause the electrochromic device to operate inthe cool mode, blocking transmittance of NIR radiation at wavelengths ofaround 780-2500 nm. In another example, application of a second negativebias voltage having a higher absolute value than the first voltage maycause the electrochromic device to operate in the dark state, blockingtransmittance of visible radiation (e.g., at wavelengths of around400-780 nm) and NIR radiation at wavelengths of around 780-1200 nm. Inanother example, application of a third voltage having a positive biasmay cause the electrochromic device to operate in the bright state,allowing transmittance of radiation in both the visible and NIR spectralregions. In various embodiments, the applied voltage may be between −5Vand 5V, preferably between −2V and 2V. For example, the first voltagemay be −0.25V to −0.75V, and the second voltage may be −1V to −2V. Inanother example, the absorbance of radiation at a wavelength of 800-1500nm by the electrochromic device may be at least 50% greater than itsabsorbance of radiation at a wavelength of 450-600 nm.

Alternatively, the nanostructure 112 and optional nanostructure 113 ofthe working electrode may modulate transmittance of NIR and visibleradiation as a function of applied voltage by operating in two differentmodes. For example, a first mode may be a highly solar transparent(“bright”) mode in which the working electrode 104 is transparent to NIRradiation and visible light radiation. A second mode may be a visibleblocking (“dark”) mode in which the working electrode 104 absorbsradiation in the visible spectral region and at least a portion of theNIR spectral region. In an example, application of a first voltagehaving a negative bias may cause the electrochromic device to operate inthe dark mode, blocking transmittance of visible and NIR radiation atwavelengths of around 780-2500 nm. In another example, application of asecond voltage having a positive bias may cause the electrochromicdevice to operate in the bright mode, allowing transmittance ofradiation in both the visible and NIR spectral regions. In variousembodiments, the applied voltage may be between −2V and 2V. For example,the first voltage may be −2V, and the second voltage may be 2V.

In various embodiments, the solid state electrolyte 106 may include atleast a polymer material and a plasticizer material, such thatelectrolyte may permeate into crevices between the transition metaloxide bronze nanoparticles 112 (and/or nanoparticles 113 if present).The term “solid state,” as used herein with respect to the electrolyte106, refers to a polymer-gel and/or any other non-liquid material. Insome embodiments, the solid state electrolyte 106 may further include asalt containing, for example, an ion species selected from the group oflanthanides (e.g., cerium, lanthanum, praseodymium, neodymium,promethium, samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium), alkali metals (e.g.,lithium, sodium, potassium, rubidium, and cesium), and alkali earthmetals (e.g., beryllium, magnesium, calcium, strontium, and barium). Inan example embodiment, such salt in the solid state electrolyte 106 maycontain a lithium and/or sodium ions. In some embodiments, the solidstate electrolyte 106 may initially contain a solvent, such as butanol,which may be evaporated off once the electrochromic device is assembled.In some embodiments, the solid state electrolyte 106 may be around 40-60wt % plasticizer material, preferably around 50-55 wt % plasticizermaterial. In an embodiment, the plasticizer material may include atleast one of tetraglyme and an alkyl hydroperoxide. In an embodiment,the polymer material of the solid state electrolyte 106 may bepolyvinylbutyral (PVB), and the salt may be lithiumbis(trifluoromethane). In other embodiments, the solid state electrolyte106 may include at least one of lithium phosphorus oxynitride (LiPON)and tantalum pentoxide (Ta₂O₅).

In some embodiments, the electrolyte 106 may include a sacrificial redoxagent (SRA). Suitable classes of SRAs may include, but are not limitedto, alcohols, nitrogen heterocycles, alkenes, and functionalizedhydrobenzenes. Specific examples of suitable SRAs may include benzylalcohol, 4-methylbenzyl alcohol, 4-methoxybenzyl alcohol, dimethylbenzylalcohol (3,5-dimethylbenzyl alcohol, 2,4-dimethylbenzyl alcohol etc.),other substituted benzyl alcohols, indoline,1,2,3,4-tetrahydrocarbazole, N,N-dimethylaniline, 2,5-dihydroanisole,etc. In various embodiments, the SRA molecules may create an air stablelayer that does not require an inert environment to maintain charge.

Polymers that may be part of the electrolyte 106 may include, but arenot limited to, poly(methyl methacrylate) (PMMA), poly(vinylbutyral-co-vinyl alcohol-co-vinyl acetate) (PVB), poly(ethylene oxide)(PEO), fluorinated co-polymers such as poly(vinylidenefluoride-co-hexafluoropropylene), poly(acrylonitrile) (PAN), poly(vinylalcohol) (PVA), etc. Plasticizers that may be part of the polymerelectrolyte formulation include, but are not limited to, glymes(tetraglyme, triglyme, diglyme etc.), propylene carbonate, ethylenecarbonate, ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate,1-butyl-3-methylimidazolium hexafluorophosphate,1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide,1-butyl-1-methyl-pyrrolidinium bis(trifluoromethane sulfonyl)imide,etc.), N,N-dimethylacetamide, and mixtures thereof.

In some embodiments, the electrolyte 106 may include, by weight, 10-30%polymer, 40-80% plasticizer, 5-25% lithium salt, and 0.5-10% SRA.

The counter electrode 108 of the various embodiments should be capableof storing enough charge to sufficiently balance the charge needed tocause visible tinting to the nanostructured transition metal oxidebronze in the working electrode 104. In various embodiments, the counterelectrode 108 may be formed as a conventional, single component film, ananostructured film, or a nanocomposite layer.

In some embodiments, the counter electrode 108 may be formed from atleast one passive material that is optically transparent to both visibleand NIR radiation during the applied biases. Examples of such passivecounter electrode materials may include CeO₂, CeVO₂, TiO₂, indium tinoxide, indium oxide, tin oxide, manganese or antimony doped tin oxide,aluminum doped zinc oxide, zinc oxide, gallium zinc oxide, indiumgallium zinc oxide, molybdenum doped indium oxide, Fe₂O₃, and/or V₂O₅.In other embodiments the counter electrode 108 may be formed from atleast one complementary material, which may be transparent to NIRradiation but which may be oxidized in response to application of abias, thereby causing absorption of visible light radiation. Examples ofsuch complementary counter electrode materials may include Cr₂O₃, MnO₂,FeO₂, CoO₂, NiO₂, RhO₂, or IrO₂. The counter electrode materials mayinclude a mixture of one or more passive materials and/or one or morecomplementary materials described above.

Without being bound to any particular theory, it is believed that theapplication of a first voltage in the various embodiments may cause theinterstitial dopant species (e.g., cesium) in the crystal structure ofthe transition metal oxide bronze to have a greater amount of freecarrier electrons and/or to cause the interstitial dopant species (e.g.,lithium ions from the electrolyte) to perform non-faradaic capacitive orpseudo-capacitive charge transfer on the surface of the nanostructures112, which may cause the surface plasmon resonance effect to increasethe absorption of NIR radiation. In this manner, the absorptionproperties of the transition metal oxide bronze characteristics maychange (i.e., increased absorption of NIR radiation) upon application ofthe first voltage. Further, application of a second voltage having ahigher absolute value than the first voltage in the various embodimentsmay cause faradaic intercalation of an intercalation dopant species(e.g., lithium ions) from the electrolyte into the transition metaloxide nanostructures. It is believed that the interaction of this dopantspecies provides interstitial dopant atoms in the lattice which createsa polaron effect. In this manner, the lattice structure of transitionmetal oxide nanoparticles may experience a polaron-type shift, therebyaltering its absorption characteristics (i.e., shift to visibleradiation) to block both visible and near infrared radiation.

In some embodiments, in response to radiation of certain spectralregions, such as UV (e.g., at wavelengths of around 10-400 nm) may causeexcitons to be generated in the polymer material of the solid stateelectrolyte 106. The UV radiation may also excite electrons in the dopedtransition metal oxide bronze to move into the conduction band, leavingholes in the valence band. The generated excitons in the polymermaterial may dissociate to free carriers, the electrons of which may beattracted to the holes in the valence band in the doped transition metaloxide bronze (e.g., cesium-doped tungsten trioxide (Cs_(x)WO₃)) ofnanoparticles 112. Since electrochemical reduction of various transitionmetal oxide bronzes by such free electron charge carriers may degradetheir performance (i.e., from unwanted coloration of the transitionmetal oxide bronze), embodiment devices may include one or more layer ofa protective material to prevent UV radiation from reaching the solidstate electrolyte 106, in addition to or instead of nanostructures 113mixed into the working electrode.

FIG. 1B illustrates an embodiment electrochromic device 150 thataddresses degradation of the doped transition metal oxide bronzenanostructures 112. Similar to device 100 shown in FIG. 1A, device 150may include a first transparent conductor layer 102 a, a workingelectrode 104, a solid state electrolyte 106, a counter electrode 108, asecond transparent conductor layer 102 b, and one or more opticallytransparent support layers 110. In addition, device 150 may include oneor more protective layers 116 a, 116 b made of a material that absorbsUV radiation. In an example embodiment, the device 150 may include afirst protective layer 116 a disposed between a first support layer 110a and the first transparent conductor layer 102 a. The device mayoptionally include a second protective layer 116 b disposed between asecond support layer 110 b and the second transparent conductor layer102 b. Alternatively, the UV protective layer 116 a may be disposed onthe outer surface of the first support layer 110 a, or may be disposedbetween the first transparent conductor 102 a and the working electrode104. In other words, the first and/or second UV protective layers 116 a,116 b may be disposed between any of the layers of the electrochromicdevice 150, such that UV light is substantially prevented from reachingthe working electrode 104.

The UV radiation absorbing material of the one or more protective layers116 a, 116 b of the various embodiments may be any of a number ofbarrier films. For example, the one or more protective layer 116 a maybe a thin film of at least one TCO material, which may include a same asor different from TCO compositions in the nanostructures 113. In anexample embodiment, a protective layer 116 a of the device 150 may be anITO thin film, and therefore capable of absorbing UV radiation byband-to-band absorption (i.e., absorption of a UV photon providingenough energy to excite an electron from the valence band to theconduction band). In another example embodiment, the device may includethe TCO nanostructures 113 made of ITO, as well as a protective layer116 a composed of an ITO thin film. Alternatively, the TCOnanostructures 113 may form a separate thin film layer 116 b disposedbetween the transition metal oxide bronze nanoparticles 112 and thetransparent conductor 102 a. In some embodiments, the UV radiationabsorbing materials of protective layers 116 a, 116 b may includeorganic or inorganic laminates.

In another embodiment, at least one UV protective layer, such asprotective layer 116 a in FIG. 1B, may be a UV radiation reflector madeof a high index transparent metal oxide. Since birds can see radiationin the UV range, a UV reflector may be implemented in embodimentspositioned as outside windows in order to prevent birds from hitting thewindows. In some other embodiments, UV radiation absorbing organicmolecules and/or inorganic UV radiation absorbing nanoparticles (e.g.,zinc oxide, indium oxide, ITO, etc.) may be incorporated within theelectrolyte 106 material.

FIG. 1C illustrates another embodiment electrochromic device 170 thataddresses degradation of the doped transition metal oxide bronzenanostructures 112 by controlling the effects of the electron chargecarriers generated in the electrolyte from exposure to UV radiation.Similar to devices 100 and 150 discussed above with respect to FIGS. 1Aand 1B respectively, device 170 may include a first transparentconductor layer 102 a, a working electrode 104, a solid stateelectrolyte 106, a counter electrode 108, a second transparent conductorlayer 102 b, and one or more optically transparent support layer 110. Inaddition, device 170 may include a protective layer 118 positionedbetween the working electrode 104 and the electrolyte 106. Theprotective layer 118 may be composed of one or more ionically conductiveand electrically insulating material.

As discussed above, without being bound to any particular theory, it isbelieved that the migration of intercalation ions between theelectrolyte 106 and the working electrode 104 is responsible for atleast some of the device's capability to modulate spectral absorption.Therefore, in order to maintain operability of the device, theelectrically insulating material used to form the protective layer 118should also be ionically conductive. That is, the material of theprotective layer 118 may prevent or reduce free electrons in the solidstate electrolyte layer 106 from reducing the transition oxide bronze ofnanoparticles 112, while allowing the diffusion of ions of anintercalation dopant species (e.g., Na, Li, etc.) between theelectrolyte 106 and working electrode 104. In an example embodiment, theelectrically insulating material that makes up the protective layer 118may be tantalum oxide, such as tantalum pentoxide (Ta₂O₅), which blocksmigration of electrons from the electrolyte 106 while allowing diffusionof the intercalation dopant species ions (e.g., lithium ions) from theelectrolyte 106. In this manner, degradation of the transition metaloxide bronze is reduced or prevented by controlling the effect of theabsorbed UV radiation in addition to or instead of instead of blockingits absorption. Other example materials that may be used to form theprotective layer 118 in addition to or instead of tantalum pentoxide mayinclude, without limitation, strontium titanate (SrTiO₃), zirconiumdioxide (ZrO₂), indium oxide, zinc oxide, tantalum carbide, niobiumoxide, and various other dielectric ceramics having similar electricaland/or crystalline properties to tantalum pentoxide.

In an alternative embodiment, instead of or in addition to theprotective layer 118, the nanostructures 112 may each be encapsulated ina shell containing an electrically insulating and ionically conductivematerial, which may be the same as or different from the material of theprotective layer 118 (e.g., tantalum oxide, strontium titanate, zincoxide, indium oxide, zirconium oxide, tantalum carbide, or niobiumoxide).

In an example embodiment, each nanostructure 112 may have a core ofcubic or hexagonal unit cell lattice structure tungsten bronze,surrounded by a shell of tantalum pentoxide.

In some embodiments, the electrolyte 106 may include a polymer thatreduces damage to the device due to UV radiation. The polymer may be anyof a number of polymers that are stable upon absorption of UV radiation(e.g., no creation of proton/electron pairs). Examples of such polymersmay include, but are not limited to, fluorinated polymers withouthydroxyl (—OH) groups (e.g., polyvinylidene difluoride (PVDF)).

In another embodiment, a positive bias may be applied to the counterelectrode 108 to draw UV radiation generated electrons from theelectrolyte 106 to the counter electrode 108 in order to reduce orprevent electrons from the electrolyte 106 from moving to the workingelectrode 104 to avoid the free electron-caused coloration of the dopedtransition metal oxide bronze in the working electrode 104.

In another embodiment, a device may include more than one of, such asany two of, any three of, or all four of: (i) a protective layer ofelectrically insulating material (e.g., protective layer 118 orprotective material shells around the bronze nanoparticles), (ii) one ormore protective layer of UV radiation absorbing material (e.g.,protective layer(s) 116 a and/or 116 b in FIG. 1B and/or UV radiationabsorbing organic molecules and/or inorganic UV radiation absorbingnanoparticles incorporated within the electrolyte 106 material), (iii)electrolyte polymer that is stable upon absorption of UV radiation,and/or (iv) application of positive bias to the counter electrode 108.In various embodiments, the nanostructures 113 may be included in oromitted from electrochromic devices 150, 170.

In another embodiment, the protective layer(s) 116 a and/or 116 b maycomprise a stack of metal oxide layers. Alternatively, the stack maycomprise a separate component that is provided instead of or in additionto the layer(s) 116 a and/or 116 b. The stack may provide improvement inthe reflected color of the electrochromic device. Prior art devicesgenerally have a reddish/purplish color when viewed in reflection. Thestack may comprise index-matched layers between the glass andtransparent conductive oxide layer to avoid the reddish/purplishreflected color. As noted above, the index-matched layer can serve asthe UV absorber or be used in addition to another UV absorber. The stackmay comprise a zinc oxide based layer (e.g., ZnO or AZO) beneath anindium oxide based layer (e.g., indium oxide or ITO).

Compared to nanocomposite electrochromic films, the various embodimentsmay involve similar production by utilizing a single nanostructuredmaterial in the working electrode to achieve the desired spectralabsorption control in both NIR and visible regions, and anothernanostructured material to enhance and expand such control in the NIRregion. Further, the various embodiments may provide one or moreadditional layer(s) of a protective material to minimize degradation ofthe single nanostructured material.

In some embodiments, the working electrode and/or the counter electrodemay additionally include at least one material, such as an amorphousnano structured material, that enhances spectral absorption in the lowerwavelength range of the visible region. In some embodiments, the atleast one amorphous nanostructured material may be at least onenanostructured amorphous transition metal oxide.

In particular, the amorphous nano structured materials may provide colorbalancing to the visible light absorption that may occur due to thepolaron-type shift in the spectral absorption of the doped-transitionmetal oxide bronze. As discussed above, upon application of the secondvoltage having a higher absolute value, the transition metal oxidebronze may block (i.e., absorb) radiation in the visible range. Invarious embodiments, the absorbed visible radiation may have wavelengthsin the upper visible wavelength range (e.g., 500-700 nm), which maycause the darkened layer to appear blue/violet corresponding to theun-absorbed lower visible wavelength range (e.g., around 400-500 nm). Invarious embodiments, upon application of the second voltage, the atleast one nanostructured amorphous transition metal oxide may absorbcomplementary visible radiation in the lower visible wavelength range(e.g., 400-500 nm), thereby providing a more even and complete darkeningacross the visible spectrum with application of the second voltage. Thatis, use of the amorphous nanostructured material may cause the darkenedlayer to appear black.

In some embodiments, at least one nanostructured amorphous transitionmetal oxide may be included in the working electrode 104 in addition tothe doped-transition metal oxide bronze nanostructures 112 and theoptional TCO nanostructures 113. An example of such material in theworking electrode 104 may be, but is not limited to, nanostructuredamorphous niobium oxide, such as niobium(II) monoxide (NbO) or otherniobium oxide materials (e.g., NbO_(x)). In some embodiments, thecounter electrode 108 may include, as a complementary material, at leastone nanostructured amorphous transition metal oxide. That is, inaddition to optically passive materials, the counter electrode 108 mayinclude at least one material for color balancing (i.e., complementing)the visible radiation absorbed in the working electrode (i.e., by thetransition metal oxide bronze. An example of such material in thecounter electrode 108 may be, but is not limited to, nanostructuredamorphous nickel oxide, such as nickel(II) oxide (NiO) or other nickeloxide materials (e.g., NiO_(x)).

In the various embodiments, nanostructures that form the working and/orcounter electrode, including the at least one amorphous nanostructuredmaterial, may be mixed together in a single layer. An example of a mixedlayer is shown in FIG. 1A with respect to transition metal oxide bronzenanostructures 112 and TCO nanostructures 113. Alternatively,nanostructures that form the working and/or counter electrode, includingthe at least one amorphous nanostructured material, may be separatelylayered according to composition. For example, a working electrode mayinclude a layer of amorphous NbO_(x) nanostructures, a layer oftransition metal oxide bronze nanostructures, and a layer of ITOnanostructures, in any of a number of orders.

The nanostructured transition metal oxide bronzes that may be part ofthe working electrode 104 in various embodiment devices can be formedusing any of a number of low cost solution process methodologies. Forexample, solutions of Nb:TiO₂ and Cs_(x)WO₃ may be synthesized usingcolloidal techniques. Compared to other synthetic methodologies,colloidal synthesis may offer a large amount of control over thenanostructure size, shape, and composition of the nanostructuredtransition metal oxide bronze. After deposition, a nanostructuredtransition metal oxide bronze material in the working electrode 104 maybe subjected to a thermal post treatment in air to remove and capligands on the surface of the nanostructures.

In various embodiments, nanostructured amorphous transition metal oxidematerials may be formed at room temperature from an emulsion and anethoxide precursor. For example, procedures used to synthesize tantalumoxide nanoparticles that are described in “Large-scale synthesis ofbioinert tantalum oxide nanoparticles for X-ray computed tomographyimaging and bimodal image-guided sentinel lymph node mapping” by M H Ohet al. (J Am Chem Soc. 2011 Apr. 13; 133(14):5508-15), incorporated byreference herein, may be similarly used to synthesize amorphoustransition metal oxide nanoparticles. For example, an overall syntheticprocess of creating the nanoparticle, as described in Oh et al., mayadopted from the microemulsion synthesis of silica nanoparticles. Insuch process, a mixture of cyclohexane, ethanol, surfactant, and acatalysis for the sol-gel reaction may be emulsified. The ethoxideprecursor may be added to the emulsion, and uniform nanoparticles may beformed by a controlled-sol gel reaction in the reverse micelles at roomtemperature within around 5 minutes. The sol-gel reaction may becatalyzed, for example, by NaOH.

In some embodiments, the nanostructured amorphous transition metal oxidemay be sintered at a temperature of at least 400° C. for at least 30minutes, such as 400 to 600° C. for 30 to 120 minutes to form a porousweb. In an example embodiment, the porous web may be included in aworking electrode 104, with the tungsten bronze nanoparticles and ITOnanoparticles incorporated in/on the web. Alternatively, the sinteringstep may be omitted and the nano structured amorphous transition metaloxide may remain in the device in the form of nanoparticles havingamorphous structure. In this embodiment, the device containing thenanostructured amorphous transition metal oxide may include or may omitthe protective layer(s) 116 a, 116 b, and 118, the UV stable electrolytepolymer, and the application of positive bias to the counter electrode.

Electrochromic responses of prepared nano structured transition metaloxide bronze materials (e.g., Cs_(x)WO₃, Nb:TiO₂, etc.) may bedemonstrated by spectro-electrochemical measurements.

In various embodiments, the shape, size, and doping levels ofnanostructured transition metal oxide bronzes may be tuned to furthercontribute to the spectral response by the device. For instance, the useof rod versus spherical nanostructures 112 may provide a wider level ofporosity, which may enhance the switching kinetics. Further, a differentrange of dynamic plasmonic control may occur for nanostructures withmultiple facets, such as at least 20 facets.

Various embodiments may also involve alternation of the nanostructures112 that form the working electrode 104. For example, the nanostructuresmay be nanoparticles of various shapes, sizes and/or othercharacteristics that may influence the absorption of NIR and/or visiblelight radiation. In some embodiments, the nanostructures 112 may beisohedrons that have multiple facets, preferably at least 20 facets.

In some embodiments, the transition metal oxide bronze nanostructures112 may be a combination of nanoparticles having a cubic unit cellcrystal lattice (“cubic nanoparticles”) and nanoparticles having ahexagonal unit cell crystal lattice (“hexagonal nanoparticles”). Eachunit cell type nanoparticle contributes to the performance of theworking electrode 104. For example, the working electrode 104 mayinclude both cubic and hexagonal cesium doped tungsten oxide bronzenanoparticles. In alternative embodiments, the working electrode 104 mayinclude either cubic or hexagonal cesium doped tungsten oxidenanoparticles. For example, the working electrode 104 may include cubiccesium-doped tungsten oxide (e.g. Cs₁W₂O_(6-x)) nanoparticles andamorphous niobium oxide nanoparticles or hexagonal cesium-doped tungstenoxide (e.g. Cs_(0.29)W₁O₃) nanoparticles without niobium oxide. Inalternative embodiments, the working electrode 104 may include undopedtungsten oxide (e.g. WO_(3-x)) nanoparticles where 0≦X≦0.1.

For example, upon application of the first (i.e., lower absolute value)voltage described above, the hexagonal bronze nanostructures 112 mayblock NIR radiation having wavelengths in the range of around 800-1700nm, with the peak absorption at the mid-NIR wavelength of around 1100nm. The cubic bronze nanostructures 112 may block NIR radiation havingwavelengths in the close-NIR range with the peak absorption of around890 nm. The indium oxide based (including ITO) and/or zinc oxide based(including AZO) nanostructures 113 may be included in the workingelectrode 104 to block the higher wavelength IR radiation uponapplication of the first voltage. Thus, the cubic bronze and hexagonalbronze nanostructures may block respective close and mid-NIR radiation(e.g., using the Plasmon effect), while the nanostructures 113 may blockthe higher wavelength IR radiation.

Upon application of the second (i.e., higher absolute value) voltagedescribed above, the cubic bronze nanostructures 112 may block visibleand NIR radiation having wavelengths in the range of around 500-1500 nm,with the peak absorption at the close-NIR wavelength of around 890 nm(e.g., using the polaron effect). Optionally, the amorphous niobiumoxide may also be added to the working electrode 104 to block the shortwavelength visible radiation (e.g., 400 to 500 nm wavelength).

The cubic bronze nanostructures block visible radiation via the polaroneffect at a lower applied voltage than the hexagonal bronzenanostructures. Thus, the second voltage may have an absolute valuewhich is below the value at which the hexagonal bronze nanostructuresblock visible radiation via the polaron effect such that thesenanostructures do not contribute to blocking of visible radiation.Alternatively, the second voltage may have an absolute value which isabove the value at which the hexagonal bronze nanostructures blockvisible radiation via the polaron effect such that these nanostructuresalso contribute to blocking of visible radiation.

Embodiment nanoparticles that form the working electrode 104 may bearound 4-6 nm in diameter, and may include 40 to 70 wt %, such as around50 wt % cubic tungsten bronze nanostructures, 15 to 35 wt %, such asaround 25 wt % hexagonal tungsten bronze nanostructures, and optionally15 to 35 wt %, such as around 25 wt % ITO nanostructures. In someembodiments, in order to achieve color balancing as described above, thenanoparticles that form the working electrode 104 may optionally includearound 5-10 wt % amorphous NbO_(x) nanostructures in place of cubictungsten bronze nanostructures. In this embodiment, the devicecontaining two types of bronze nanoparticles may include or may omit theprotective layer(s) 116 a, 116 b, and 118, the UV stable electrolytepolymer, the application of positive bias to the counter electrode, andthe amorphous niobium oxide.

In summary, the working electrode 104 may include one or more of thefollowing components:

-   -   (a) metal oxide bronze nanostructures 112 having (i) a        cubic, (ii) hexagonal, or (iii) a combination of cubic and        hexagonal unit cell lattice structure;    -   (b) protective (i) indium oxide based (including ITO) and/or        zinc oxide based (including AZO) nanostructures 113;    -   (c) amorphous niobium oxide nanoparticles and/or web; and/or    -   (d) additional nanostructures selected from undoped tungsten        oxide, molybdenum oxide, titanium oxide, and/or vanadium oxide.

The counter electrode 108 may include one or more of the followingcomponents:

-   -   (a) passive electrode material selected from cerium(IV) oxide        (CeO₂), titanium dioxide (TiO₂), cerium(III) vanadate (CeVO₂),        indium(III) oxide (In₂O₃), tin-doped indium oxide, tin(II) oxide        (SnO₂), manganese-doped tin oxide, antimony-doped tin oxide,        zinc oxide (ZnO), aluminum-doped zinc oxide (AZO), iron(III)        oxide (Fe₂O₃), and vanadium(V) oxide (V₂O₅);    -   (b) an active electrode material selected from chromium(III)        oxide (Cr₂O₃), manganese dioxide (MnO₂), iron(II) oxide (FeO),        cobalt oxide (CoO), nickel(II) oxide (NiO), rhodium(IV) oxide        (RhO₂), and iridium(IV) oxide (IrO₂);    -   (c) amorphous nickel oxide nanoparticles and/or web; and/or    -   (d) conductivity enhancer nanoparticles selected from indium        oxide, ITO, and zinc oxide.

While the various embodiments are described with respect toelectrochromic windows, the embodiment methods, systems, and devices mayalso be used in materials for other types of smart windows. Such smartwindows may include, but are not limited to, polymer-dispersed liquidcrystals (PLDD), liquid crystal displays (LCDs), thermochromics, etc.

Color Tunability

Color tunability of electrochromic devices is applicable to a variety ofapplications. According to various embodiments, the present disclosureprovides electrochromic devices having the capability of achieving amultitude of colors that may not currently be available in the market.The technique for achieving color tunability in one embodiment is basedon the selection of the composition and the deposition of the activematerials. While colored glass may be achieved by the use of doped glass(e.g., glass with metal impurities added to impart color), this is anon-standard product from most primary glass manufacturers on theirfloat lines, and this entails cost premium. By contrast, the presentlydisclosed color tunability can be achieved in a nearly cost-neutralfashion, as the nanostructures can be synthesized for approximately thesame cost for devices of different colors.

According to various embodiments, the present disclosure allows color ofelectrochromic devices to be tuned by utilizing various nanostructurecompositions, or mixtures thereof, in the active, i.e. working,electrode of an electrochromic device. In particular, depending on thenanostructure components used and/or a ratio therebetween, a wide rangeof colors may be achieved, such as, for example, gray, blue, green,purple, and brown, but the present disclosure is not limited thereto.For example, an electrochromic device may include a working electrodeincluding a variety of metal oxide nanostructures, such as nanocrystalsand amorphous metal oxide nanoparticles. Such nanostructures may includeWO₃, Cs_(x)WO₃ (where 0.2≦x≦0.4, e.g., 0.29≦x≦0.31), Cs₁WO_(6-σ) (where0≦σ≦0.3), NbO_(x), TiO₂, MoO₃, NiO₂, V₂O₅, or combinations thereof.

FIG. 2 is a schematic representation of an electrochromic device 180that may be configured to produce a particular color, according tovarious embodiments or the present disclosure. The electrochromic device180 is similar to the electrochromic device 150 of FIG. 1B, so only thedifferences therebetween will be discussed in detail.

Referring to FIG. 2, the electrochromic device 180 includes a workingelectrode 104. In particular, the working electrode 104 may includevarious nanostructures as discussed above, in order to producecorresponding colors. For example, the working electrode may includefirst nanostructures 115 and/or second nanostructures 117, according toa particular color the working electrode 104 is configured to form. Inother words, the second nanostructures 117 may be omitted, or additionalnanostructures may be added.

For example, in order to produce a blue color, the working electrode 104may include about 100 wt. % of WO₃ as the first nanostructures 115 andmay omit the second nanostructures 117. In order to produce a greencolor, the working electrode 104 may include about 60 wt. % ofCs_(x)WO₃, such as Cs_(0.29)WO₃, hexagonal crystal lattice structurenanocrystals as the first nanostructures 115, and about 40 wt. % ofindium tin oxide (e.g., Sn:In₂O₃) nanocrystals as the secondnanostructures 117.

In order to produce a brown color, the working electrode 104 may includeabout 100 wt. % NbO_(x) nanoparticles (e.g., Nb₂O_(5-σ) where 0≦σ≦0.1)as the first nanostructures 115 and may omit the second nanostructures117. In order to produce a purple color, the working electrode 104 mayinclude about 100 wt. % Nb:TiO₂ nanocrystals as the first nanostructures115 and may omit the second nanostructures 117.

According to various embodiments, the present inventors discovered thatelectrochromic devices that produce a neutral gray color may beunexpectedly advantageous. In particular, since the human eye is lesssensitive with respect to detecting variations in neutral gray colors,as compared to variations in other colors, color variations in adjacentelectrochromic devices that produce neutral gray colors are lessnoticeable to the human eye. As such, tone variations between adjacentelectrochromic devices producing a neutral gray color may be greaterthan for other colors, without being noticeable to the human eye.

For example, in order to produce a neutral gray color, the firstnanostructures 115 may include amorphous niobium oxide (“NbO_(x)”)nanoparticles (e.g., Nb₂O_(5-σ) where 0≦σ≦0.1), and the secondnanostructures 117 may include cesium doped tungsten oxide (“CWO”)nanoparticles having a cubic crystal lattice structure (e.g.,CsW₂O_(6-σ) nanocrystals, where 0≦σ≦0.3). Herein, the CWO nanoparticlesmay be referred to as “nanocrystals”, due to their crystallinestructure. The relative amounts of the NbO_(x) nanoparticles and CWOnanocrystals included in the working electrode 104 may result invariations in the color of the working electrode 104.

In particular, the working electrode 104 may include a nanostructuredlayer comprising from about 40 to about 80 wt. % of the NbO_(x)nanoparticles and from about 60 to about 10 wt. % of the CWOnanocrystals. In other embodiments, the working electrode 104 mayinclude from about 65 to about 80 wt. % of the NbO_(x) nanoparticles andfrom about 35 to about 20 wt. % of the CWO nanocrystals. In someembodiments, the working electrode may include from about 40 to 50 wt. %of the NbO_(x) nanoparticles and from about 60 to about 50 wt. % of theCWO nanocrystals.

According to various embodiments, the NbO_(x) nanoparticles may have anaverage particle size of from about 2 to about 6 nm, such as from about3 to about 5 nm. For example, the NbO_(x) nanoparticles may have anaverage particle size of about 4 nm. The CWO nanocrystals may have anaverage particle size of from about 3 to about 7 nm, such as from about4 to about 6 nm. For example, the CWO nanocrystals may have an averageparticle size of about 5 nm.

According to other embodiments, the working electrode 104 may include ananostructured layer comprising a mixture of amorphous molybdenum oxidenanoparticles (“MoO₃”) and tungsten oxide nanocrystals (“WO₃”), in orderto produce a neutral gray color. In particular, the working electrode104 may include a nanostructured layer comprising from about 40 to about80 wt. % of the MoO₃ nanoparticles and from about 60 to about 10 wt. %of the WO₃ nanocrystals. In other embodiments, the working electrode 104may include from about 65 to about 80 wt. % of the MoO₃ nanoparticlesand from about 35 to about 20 wt. % of the WO₃ nanocrystals. In someembodiments, the working electrode may include from about 40 to 50 wt. %of the MoO₃ nanoparticles and from about 60 to about 50 wt. % of the WO₃nanocrystals.

According to some embodiments, the working electrode 104 may include ananostructured layer comprising molybdenum doped tungsten oxidenanocrystals. For example, the molybdenum doped tungsten oxidenanocrystals may be represented by the general formula Mo_(x)WO₃ (where0.1≦x≦0.75, e.g., 0.2≦x≦0.5).

EXEMPLARY EMBODIMENTS

FIG. 3A includes photographs of electrochromic devices including workingelectrodes having the various amounts of NbO_(x) nanoparticles (e.g.,40, 50, 60, 70, 80, 90, and 100 wt. %) and corresponding amounts CWOnanocrystals (e.g., 60, 50, 40, 30, 20, 10, and 0 wt. %) to equal 100wt. %. FIG. 3B is a graph showing the color spectra of light transmittedthrough (i.e., fraction transmittance as a function of radiationwavelength) corresponding electrochromic devices of FIG. 3A in theirdark state.

Referring to FIG. 3A, in the top row, the electrochromic devices areshown in a bright mode, and in the bottom row the electrochromic devicesare shown in a dark mode. In addition, the working electrodes of theelectrochromic devices are produced using aqueous-based inks containingthe corresponding nanostructures. However, according to someembodiments, the inks may include an organic solvent rather than water.The inks may be coated at 50-200 mg/ml, such as 100 mg/ml, to preventhaze formation. The numbers in the bottom row indicate approximateworking electrode thickness.

As can be seen in FIGS. 3A and 3B, the electrochromic devices includingfrom about 40 to about 80 wt. % of the NbO_(x), nanoparticles, and fromabout 60 to about 20 wt. % of the CWO nanocrystals, produced graycolors, with 40-50 wt. % NbO_(x), nanoparticles and an aqueous solventproducing neutral gray colors. In addition, lower amounts of the NbO_(x)nanoparticles than 40 wt. % resulted in a more bluish color, whileamounts of the NbO_(x) nanoparticles higher than 80 wt. % producedbrownish colors in the bright mode.

Further, the following Table 1 shows results of charge transfer testsperformed on the devices of FIG. 3A.

TABLE 1 NbO_(x) (wt. %) 100 90 80 70 60 50 40 Thick- 300-400 250-300300-350 100 300-400 200-300 300-400 ness (mm) Charge 25 25 25 N/A 25 2535 Transfer (mC/ cm²)

However, for an organic solvent, 65-75 wt. % NbO_(x), nanoparticles,e.g., about 70 wt. % NbO_(x) nanoparticles, results in neutral graycolors.

FIGS. 4A and 4B are photographs of a fabricated electrochromic device180A in a bright mode and a dark mode, respectively, according tovarious embodiments. FIG. 4C is a graph illustrating the transmittancefraction as a function of wavelength, when the device 180A is in thebright mode (+2V applied to the electrodes) and the dark mode (−2Vapplied to the electrodes).

Referring to FIGS. 4A-4C, the device 180A includes a working electrodehaving a thickness of from 600-800 nm and that comprises 40 wt. %NbO_(x) nanoparticles and 60 wt. % CWO nanocrystals. The device 180Aalso includes a counter electrode having a thickness of about 1.6 μm andthat comprises about 25 wt. % In₂O₃ and about 75 wt. % ceria (cerium(IV)oxide (CeO₂)).

In addition, the device 180A had reflectance and transmittance colorcoordinates as shown in the following Tables 2 and 3.

TABLE 2 (Reflectance Color) Operation L* A* B* Bright Mode 77.42 −2.040.4 Dark Mode 24.36 1.3 −4.32

TABLE 3 (Transmittance Color) Operation L* A* B* Bright Mode 77.42 −2.043.9 Dark Mode 33.39 2.27 −3.03

FIGS. 5A and 5B are photographs of an electrochromic device 180B in abright mode and a dark mode, respectively, according to variousembodiments of the present disclosure. FIG. 5C is a graph illustratingtransmittance of the electrochromic device 180B in the bright mode, thedark mode, and a transition mode where the device 180B is transitioningbetween the dark and bright modes.

Referring to FIGS. 5A and 5B, the electrochromic device 180B is a 4″device which is similar to the electrochromic device 180 of FIG. 2,except for including an active electrode comprising a nanostructuredlayer comprising about 70 wt. % NbO_(x) nanoparticles and 30 wt. % CWOnanocrystals deposited using an organic solvent. The device 180B alsoincludes a counter electrode having a thickness of about 1.6 μm and thatcomprises 25 wt. % In₂O₃ and 75 wt. % ceria (cerium(IV) oxide (CeO₂)).The NbO_(x) nanoparticles are amorphous and have an average particlesize of about 4 nm. The CWO nanocrystals are cubic and have an averageparticle size of about 5 nm. Thus, as shown in FIG. 11A, the device 180Bis configured to exhibit a neutral gray color in the bright mode.

As shown in FIG. 5C, the electrochromic device 180B transmits at least50%, such as at least 60%, e.g., 60-65% of received light in the 400-800nm wavelength visible range, when in the bright mode. In addition, whenin the dark mode, the electrochromic device 180B blocks about 95% oflight in the visible range.

The following Table 4 includes transmission and reflection colorcoordinates of the electrochromic device 180B.

TABLE 4 Visible EC Attributes Performance Transmitted Color (Bright)(−5.0A*, 4.6B*)  Transmitted Color (Transition) (−4.8A*, −2.3B*)Transmitted Color (Dark) (−1.9A*, 0.6B*)  Reflected Color (Bright)(−2.5A*, −0.1B*) Reflected Color (Transition) (−0.8A*, −2.8B*) ReflectedColor (Dark)  (0.1A*, −2.3B*)

FIGS. 6A and 6B are Lab color coordinate graphs respectively showingtransmission color coordinate boxes and outdoor reflection colorcoordinate boxes, corresponding to an electrochromic device having aneutral gray color, according to various embodiments of the presentdisclosure.

Referring to FIG. 6A, the color box includes acceptable colorcoordinates for light transmitted through the electrochromic device,while the device is in at least one of a bright mode, a transition mode,and a dark mode. In particular, the color box includes A* coordinatesranging from about zero to about −4.0, and B* coordinates ranging fromabout 4.0 to about −2.0. In addition, a preferred color box includes A*coordinates ranging from about −1.0 to about −3.0, and B* coordinatesranging from about zero to about 2.0. According to some embodiments,light transmitted through the electrochromic device during both thebright mode and the dark mode may have color coordinates in the colorbox and/or the preferred color box. In some embodiments, an on-axis, 90degree observed color may be in the center of the color box e.g., atA*−2, B*1. In addition, colors observed at other angles may also bepresent in the color box.

According to various embodiments, transmittance color variations (ΔE)within/between electrochromic devices may be measured using thefollowing formula: ΔE=√((ΔA*)²+(ΔB*)²), wherein ΔA*=A1*−A2*, andΔB*=B1*−B2*. In particular, for two points having the same L value, thetransmittance color variation ΔE therebetween may be less than about4.0, such as less than about 3.5, or less than about 3.0, e.g., 0.1-3.0or zero −3.5.

Referring to FIG. 6B, the color box represents acceptable colorcoordinates produced by external, e.g., outdoor, reflections from theelectrochromic device, while the device is in at least one of brightmode, transition mode, and dark mode. In particular, the colorcoordinate box includes A* coordinates ranging from about 1.0 to about−5.0, and B* coordinates ranging from about zero to about −8.0. Inaddition, a preferred color box includes A* coordinates ranging fromabout −1.0 to about −3.0, and B* coordinates ranging from about −3.0 toabout −5.0. According to some embodiments, light reflected from theelectrochromic device during both the bright mode and the dark mode mayhave color coordinates in the color box and/or the preferred color box.In some embodiments, an on-axis, 90 degree observed color may be in thecenter of the color box, e.g., at A*−2, B*-4. In addition, colorsobserved at other angles may also be present in the color box.

According to various embodiments, reflectance color variations (ΔE)within/between electrochromic devices may be measured using thefollowing formula: ΔE=√((ΔA*)²+(ΔB*)²), wherein ΔA*=A1*−A2*, andΔB*=B1*−B2*. In particular, for two points having the same L value, thereflectance color variation ΔE therebetween may be less than about 3.0,such as less than about 2.5, or less than about 2.0. e.g., 0.1-2.0 orzero −2.5.

According to some embodiments, an electrochromic device may have atransmitted haze of less than about 1.0%, such as less than about 0.75%,or less than about 0.5%, e.g., 0.1%-0.4% or 0% to 0.5%. As such, thepresent disclosure provides electrochromic devices that haveunexpectedly reduced transmitted haze, as compared to conventionalelectrochromic devices, which may have a transmitted haze of 2% to 2.5%,or more.

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

The invention claimed is:
 1. An electrochromic device, comprising: afirst transparent conductor layer; a working electrode disposed on thefirst transparent conductor layer and comprising nanostructures, thenanostructures comprising at least about 40 wt. % of amorphous niobiumoxide nanoparticles and about 60 wt. % or less of tungsten oxidenanoparticles having a cubic crystal lattice structure, based on thetotal weight of the nanostructures; a counter electrode; a solid stateelectrolyte layer disposed between the counter electrode and the workingelectrode; and a second transparent conductor layer disposed on thecounter electrode.
 2. The electrochromic device of claim 1, wherein; thenanostructures comprise from about 40 to about 80 wt. % of the amorphousniobium oxide nanoparticles and from about 60 to about 20 wt. % of thetungsten oxide nanoparticles, based on the total weight of thenanostructures; and the tungsten oxide nanoparticles are doped withcesium and have a cubic crystal lattice structure.
 3. The electrochromicdevice of claim 2, wherein the working electrode comprises: from about35 to about 25 wt. % of the cesium doped tungsten oxide nanoparticles;and from about 65 to about 75 wt. % of the amorphous niobium oxidenanoparticles.
 4. The electrochromic device of claim 1, wherein: theamorphous niobium oxide nanoparticles have an average particle size offrom about 3 nm to about 5 nm; and the tungsten oxide nanoparticles havean average particle size of from about 4 nm to about 6 nm.
 5. Theelectrochromic device of claim 1, further comprising a protective layerconfigured to reduce degradation of the nanostructured layer due toultraviolet (UV) radiation.
 6. The electrochromic device of claim 1,wherein: the electrochromic device has a transmitted haze of less thanabout 1.0%; in a bright mode the electrochromic device transmits atleast 50% of received visible light; and in a dark mode theelectrochromic device transmits 5% or less of received visible light. 7.The electrochromic device of claim 1, wherein the counter electrodecomprises at least one selected from: CeO₂; CeVO₂; TiO₂; indium tinoxide; indium oxide; tin oxide; manganese or antimony doped tin oxide;aluminum doped zinc oxide; zinc oxide; gallium zinc oxide; indiumgallium zinc oxide; molybdenum doped indium oxide; Fe₂O₃; and V₂O₅. 8.The electrochromic device of claim 1, wherein: the working electrode isconfigured such that the electrochromic device transmits light of afirst color in a bright mode and a second color in a dark mode; and atleast one of the first color and the second color is disposed in a firstLab color coordinate box having A* color coordinates ranging from aboutzero to about −4.0, and B* color coordinates ranging from about 4.0 toabout −2.0.
 9. The electrochromic device of claim 8, wherein at leastone of the first color and the second color is disposed in a second Labcolor coordinate box having A* color coordinates ranging from about −1.0to about −3.0, and B* color coordinates ranging from about zero to about2.0.
 10. An electrochromic device comprising: a first transparentconductor layer; a working electrode disposed on the first transparentconductor layer and comprising nanostructures comprising nanoparticlesconfigured such that the electrochromic device transmits light of afirst color in a bright mode and a second color in a dark mode; acounter electrode; a solid state electrolyte layer disposed between thecounter electrode and the working electrode; and a second transparentconductor layer disposed on the counter electrode, wherein at least oneof the first color and the second color is disposed in a first Lab colorcoordinate box having A* color coordinates ranging from about zero toabout −4.0, and B* color coordinates ranging from about 4.0 to about−2.0.
 11. The electrochromic device of claim 1, wherein thenanostructures comprise molybdenum doped tungsten oxide nanoparticles.12. The electrochromic device of claim 1, wherein the electrochromicdevice is located in a window.
 13. The electrochromic device of claim10, wherein the nanostructures comprise at least about 40 wt. % ofamorphous molybdenum oxide nanoparticles and about 60 wt. % or less oftungsten oxide nanoparticles, based on the total weight of thenanostructures.
 14. The electrochromic device of claim 10, wherein bothof the first color and the second color are disposed in the first Labcolor coordinate box.
 15. The electrochromic device of claim 10, whereinat least one of the first color and the second color is disposed in asecond Lab color coordinate box having A* color coordinates ranging fromabout −1.0 to about −3.0, and B* color coordinates ranging from aboutzero to about 2.0.
 16. The electrochromic device of claim 15, whereinboth of the first color and the second color are disposed in the secondLab color coordinate box.
 17. The electrochromic device of claim 10,wherein: the nanostructures are configured such that the electrochromicdevice reflects outdoor light of a third color in the bright mode and afourth color in the dark mode; and at least one of the third color andthe fourth color is disposed in a third Lab color coordinate box havingA* color coordinates ranging from about 1.0 to about −5.0, and B* colorcoordinates ranging from about zero to about −8.0.
 18. Theelectrochromic device of claim 17, wherein both of the third color andthe fourth color are disposed in the third Lab color coordinate box. 19.The electrochromic device of claim 17, wherein at least one of the thirdcolor and the fourth color is disposed in a fourth Lab color coordinatebox having A* color coordinates ranging from about −1.0 to about −3.0,and B* color coordinates ranging from about −3.0 to about −5.0.
 20. Theelectrochromic device of claim 19, wherein both of the third color andthe fourth color are disposed in the fourth Lab color coordinate box.21. The electrochromic device of claim 10, wherein the first color is aneutral gray color.
 22. The electrochromic device of claim 10, wherein:the electrochromic device has a transmitted haze of less than about1.0%; in a bright mode the electrochromic device transmits at least 50%of received visible light; and in a dark mode the electrochromic devicetransmits 5% or less of received visible light.
 23. The electrochromicdevice of claim 10, wherein the electrochromic device is located in awindow.
 24. A method of operating an electrochromic device, comprising:operating the device in a bright mode, such that the device transmitslight of a first color; and operating the device in a second mode, suchthat the device transmits light of a second color, wherein at least oneof the first color and the second color is disposed in a first Lab colorcoordinate box having A* color coordinates ranging from about zero toabout −4.0, and B* color coordinates ranging from about 4.0 to about−2.0.
 25. The method of claim 24, wherein both of the first color andthe second color are disposed in the first Lab color coordinate box. 26.The method of claim 24, wherein at least one of the first color and thesecond color is disposed in a second Lab color coordinate box having A*color coordinates ranging from about −1.0 to about −3.0, and B* colorcoordinates ranging from about zero to about 2.0.
 27. The method ofclaim 26, wherein both of the first color and the second color aredisposed in the second Lab color coordinate box.
 28. The method of claim24, wherein: operating the device in the bright mode further comprisesreflecting outdoor light of a third color; operating the device in thedark mode further comprises reflecting outdoor light of a fourth color;and at least one of the third color and the fourth color is disposed ina third Lab color coordinate box having A* color coordinates rangingfrom about 1.0 to about −5.0, and B* color coordinates ranging fromabout zero to about −8.0.
 29. The method of claim 28, wherein both ofthe third color and the fourth color are disposed in the third Lab colorcoordinate box.
 30. The method of claim 28, wherein at least one of thethird color and the fourth color is disposed in a fourth Lab colorcoordinate box having A* color coordinates ranging from about −1.0 toabout −3.0, and B* color coordinates ranging from about −3.0 to about−5.0.
 31. The method of claim 30, wherein both of the third color andthe fourth color are disposed in the fourth Lab color coordinate box.32. The method of claim 28, wherein: the first color is a neutral graycolor; the electrochromic device has a transmitted haze of less thanabout 1.0%; in a bright mode the electrochromic device transmits atleast 50% of received visible light; and in a dark mode theelectrochromic device transmits 5% or less of received visible light.33. The method of claim 24, wherein the electrochromic device is locatedin a window.